Evaluation of Distinctive Oil Bores in Engine Crankshaft for Friction Reduction Purpose 2023-32-0160

Internal combustion engines will play an important role in the coming decades, even considering targets of carbon neutrality for a sustainable future. This will be especially true in regions where pure electrified vehicle implementation is not yet practical, or for long-range heavy load transportation purposes, even in regions where BEV infrastructure is well established.

HEV/PHEV’s importance and contribution to CO2 emission reduction together with carbon neutral fuels such as hydrogen, e-fuel and biomass fuel etc. will remain crucial regardless of region/transport sectors. In this respect, brake thermal efficiency improvements by friction reduction needs further investigation. This is especially so with the crankshaft bearings’ lubrication system, which can provide as much as 40% of the total mechanical losses in some cases.

It is a well-established fact, that plain bearings require a minimum oil flow volume to maintain their real function rather than oil pressure. However, transportation of oil to the connecting-rod bearings, from the crank main journals, via a rotating oil supply hole inside the crankshaft, requires a certain minimum pressure in order to cope with centrifugal force. Additionally, the pressure drop caused by oil flow needs to be considered.

An important aspect to lower the oil pressure requirement while maintaining requisite oil flow to the connecting-rod bearings, is the oil supply hole to crank rotating axis distance. This practice is already exploited in some racing engine crankshafts, which require higher rotation speeds than normal road use engines. Furthermore, minimizing oil leaks from bearings can enhance the bearing lubrication system’s efficiency. In order to overcome this dilemma and optimize the crankshaft bearing system, a distinct oil supply hole arrangement is adopted in the crankshaft. This crankshaft has oil supply holes far from the rotation axis and the crank pin oil outlet ports close to the crank axis. This crankshaft also has four inlet ports in the main journal, that additionally exploit dynamic pressure from crankshaft rotation. To explain this, the crankshaft is evaluated on an engine test bench and its friction reduction potential was quantified by analysing the test results.